Enhanced charge separation in g-CN-BiOI heterostructures for visible light driven photoelectrochemical water splitting.

Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-CN) and few layered graphitic carbon nitride sheets (g-CN-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting. HR-TEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and the carbon nitride (g-CN and g-CN-S) network that consisted of dendritic BiOI nanoplates surrounded by g-CN sheets. The presence of BiOI in g-CN-S/BiOI and g-CN-S/BiOI nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent charge separation in g-CN/BiOI and g-CN-S/BiOI, evident from quenching of the carbon nitride photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical performance is observed for both types of g-CN-BiOI heterojunctions. In comparison to heterojunctions of bulk g-CN with BiOI, the nanocomposite consisting of few layered sheets of g-CN and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A synergistic trap passivation and charge separation is found to occur in the g-CN-S/BiOI nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer resistance.